1. Field of the invention
The present invention generally relates to a toner supply device for a developing device adapted for an image forming apparatus such as a copying machine, a printer or the like.
2 Description of the related art
Conventionally, there is a type of a toner supply device which comprises a hopper arranged above the developing device for containing toner therein and a toner supply roller disposed at an opening which is formed at a bottom of the hopper so as to fill the opening, the toner supply roller having slotted grooves which are formed on its outer surface as well as in the direction of its axis. In this type of the toner supply device, by rotating the toner supply roller occasionally, the toner in the hopper may be got into the slotted groove while the slotted groove faces the hopper, and the toner in the slotted grooves falls into the developing device when the groove moves to its bottom position.
For example, the device which has been disclosed in the Japanese Laid-open Utility Model Publication No. 59-51355 (1984) has a scraper of an elastic material, whereby the toner accumulated in slotted grooves which are formed on a toner supply roller is scraped out.
Further, another devices have been, respectively, disclosed in the Japanese Laid-open Utility Model Publication Nos. 59-51356 (1984) and 59-51357 (1984). These device have a brush, whereby the toner accumulated in slotted grooves which are formed on a toner supply roller is brushed off.
Further, another device has disclosed in the Japanese Laid-open Utility Model Publication No. 60-14277 (1985). The device has a toner supply roller on which slotted grooves for supplying toner are intermittently formed along the longitudinal direction of the roller, and a regulating blade for preventing unnecessary toner from leaking is kept in close contact under pressure with the peripheral surface of the toner supply roller.
However, in the former design that is to utilize the toner supply roller having the slotted grooves, it may happen that the toner to be supplied to the developing device adheres to the grooves and remains therein, or the toner accumulated in the groove falls down all of a lump to the inside of the developing device, thus resulting in that dispersion of the toner accommodated in the developing device becomes worse, so that it may be caused that the toner is not sufficiently charged. In addition to the above, various types of shielding members to be arranged on the peripheral portion and/or shaft end portion of the toner supple roller are required so as to prevent unnecessary toner from leaking to the developing device. As a result of that, it may give rise to complication of the device and increase of power for driving the toner supply roller since shielding by the shielding member can be sufficiently tough because of the slotted grooves on the surface of the roller.
So as to improve these disadvantages and carry out stable supply of the toner, another design has been disclosed. That is to form a thin layer of the toner on a toner supply roller and to scrape off the thin layer and then to supply that to a developing device.
For example, a device disclosed in the Japanese Laid-open Patent Publication No. 59-34563 (1984) includes a toner supply roller made of a magnetic roller. Therefore, the toner particles having magnetism cling to the surface of the roller, and these take the form of a thin layer on the roller. In the device, it is so designed that the thin layer of the toner is scraped off by a scraper and the toner is fallen into a developing device. At this moment, a thickness of the layer of the toner is adjustable by a member for regulating a supplied quantity of the toner.
Another type of a device has been disclosed in the Japanese Laid-open Patent Publication No. 56-151960 (1981). In this device, a toner supply roller has minute concave and convex portions on its surface. A layer of a developer formed thereon is brushed off by a brush-shape member, and then the developer is supplied into a developing device.
In these types of the devices, however, there are another disadvantages. That is, the toner or the developer is to be dispersed and charged in the developing device by agitation after the toner is fallen down and supplied to the developing device. Accordingly, it may give rise to unsufficiently charging of the toner or the developer, or something like that.
In order to improve the above-mentioned disadvantages, another type of a device is disclosed which is designed in such way that a pre-discharged toner layer is formed on a toner supply roller and the layer is made to scrape off and, then, the toner is supplied into a developing device.
For example, this type of a device disclosed in the Japanese Laid-open Utility Model Publication No. 61-99169 (1986) is designed as follows. The device has a charging blade and a scraping blade, both blades being kept in close contact under pressure with a toner supply roller, wherein toner is pre-charged by contact with a friction between the charging blade and the toner as well as the toner is fallen down into a developing device by the scraping blade. In this toner supply device, however, the toner passed through the charging blade once is immediately scraped off by the scraping blade. Therefore, it is not always to obtain the result that pre-charging of the toner can be made enough.
Generally, in the developing device, the toner is not always consumed uniformly along the direction of the width of a developing section since, normally, a size of an original document image is different and density of that is not uniform. Therefore, in the toner supply device described previously, it may happen that the toner is supplied to the developing section in which the toner is not required, thus resulting in that it may happen that image density does not become uniform.
In addition, the conventional type of the toner supply devices described previously have the below-mentioned disadvantage caused by these structure. That is, the toner supply roller is triboelectrically charged when it rotates under the condition that the roller is kept in contact with the scraping blade and so on, and then, the charge is accumulated on the peripheral surface of the roller. As a result of that, electrification of the toner given by contact having friction with the charging blade becomes low, and scraping efficiency by the scraping blade becomes worse as well, so that there happens a problem that the toner is not uniformly supplied.